How to counter Gren spam with shrecks ?

So i've been constantly playing vs cousin, (Brits v Wehr) and most of the time i have won, but then he started to play 5 piosinto Gren spam with shrecks. i tried almost everything, when i cut him off the strat points, he raids my base. When i play def at my base he purely overwhelms me due to his numbers, since Grens are cheaper than IF but are equal to them.

So is there any common strategy against this ? I'll be very glad for every tip.